A vehicle, such as an automobile, includes a steering system for controlling a traveling direction. In general, an operation mechanism of such a steering system includes, for example, a steering wheel used by an occupant to control the steering angle, a steering shaft for transmitting the rotation of the steering wheel to a gear box, a steering column for supporting the steering shaft, a column cover covering the steering column, and a turn signal switch unit for operating a turn signal.
The steering wheel includes an annular rim section, a boss section that forms a joint portion with the steering shaft, a plurality of spoke sections that connect the boss section and the rim section, and a pad section provided at almost the center of the boss section. The pad section includes an airbag cover that forms a front surface, and an airbag device and a horn switch are provided within the airbag cover. A typical airbag device includes an airbag that is normally folded and is inflated and deployed in an emergency, an inflator for supplying gas to the airbag, and a retainer for fixing the airbag and the inflator. The airbag device and the airbag cover are generally fixed by fixing the retainer to a side wall portion standing on a back side of the airbag cover (see, for example, PTL 1 and PTL 2).
For example, an airbag device described in PTL 1 includes a support member (base plate) for supporting an airbag, and a cover body attached to the support member to cover the folded airbag. The support member includes inner engaging portions to be engaged with an inner side of the cover body, and an outer engaging portion to be engaged with an outer side of the cover body. Here, the airbag is attached to the base plate by inserting attachment bolts provided integrally with a preset retainer in attachment holes of the airbag, exposing them from attachment holes of the base plate, and fixing them with by nuts. The cover body can be firmly held by the inner engaging portions and the outer engaging portion formed integrally with the support member so that the cover body does not internally and externally deform and fall off. This can reduce the number of components, the cost, and the weight of the airbag device.
An airbag device described in PTL 2 is an example of an airbag device including a retainer that clamps and combines a cover member for housing an inflator and a folded airbag by using assist plates and fasteners. In a driver airbag device, a cover body and a retainer are often fastened together by using assist plates and fasteners (for example, rivets), as described in PTL 2.